U.S. patent number 7,710,065 [Application Number 11/876,971] was granted by the patent office on 2010-05-04 for power conversion system and power conversion control method.
This patent grant is currently assigned to Nissan Motor Co., Ltd.. Invention is credited to Kengo Maikawa, Yuki Nakajima, Sho Sato, Kantaro Yoshimoto.
United States Patent |
7,710,065 |
Sato , et al. |
May 4, 2010 |
Power conversion system and power conversion control method
Abstract
A power conversion system includes first and second voltage
sources for driving a multiple-phase AC motor and a control unit.
The control unit is configured to compute first and second output
voltage command values used to drive the multiple-phase AC motor
based on a first output voltage command vector corresponding to the
voltage source that is charged and a second output voltage command
vector corresponding to the voltage source that is discharged. The
first and second output voltage command vectors are determined so
that a resultant vector of the first and second output voltage
command vectors is coincident with a motor voltage command vector
corresponding to a motor voltage command value, and a motor current
command vector corresponding to the motor current command value is
positioned within an included angle formed between the second
output voltage command vector and a negative vector of the first
output voltage command vector.
Inventors: |
Sato; Sho (Yokohama,
JP), Yoshimoto; Kantaro (Yokohama, JP),
Maikawa; Kengo (Yokosuka, JP), Nakajima; Yuki
(Yokohama, JP) |
Assignee: |
Nissan Motor Co., Ltd.
(Yokohama, JP)
|
Family
ID: |
39608091 |
Appl.
No.: |
11/876,971 |
Filed: |
October 23, 2007 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20080258662 A1 |
Oct 23, 2008 |
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Foreign Application Priority Data
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Nov 17, 2006 [JP] |
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2006-311857 |
Oct 9, 2007 [JP] |
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2007-263365 |
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Current U.S.
Class: |
318/801; 363/71;
318/812; 307/43 |
Current CPC
Class: |
H02J
3/38 (20130101); H02J 1/102 (20130101) |
Current International
Class: |
H02P
21/00 (20060101); H02J 1/10 (20060101); H02M
7/5387 (20070101) |
Field of
Search: |
;318/34,801-812,599
;363/41,71,98,132,142 ;307/43,75,80,81 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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1615325 |
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Jan 2006 |
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EP |
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S54-119609 |
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Sep 1979 |
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JP |
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2006-033956 |
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Feb 2006 |
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JP |
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2006-166588 |
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Jun 2006 |
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JP |
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2006-166596 |
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Jun 2006 |
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JP |
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2006-166628 |
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Jun 2006 |
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JP |
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2006-246617 |
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Sep 2006 |
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JP |
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2006-296040 |
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Oct 2006 |
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JP |
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WO2006/061679 |
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Jun 2006 |
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WO |
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Primary Examiner: Benson; Walter
Assistant Examiner: Colon; Eduardo
Attorney, Agent or Firm: Global IP Counselors, LLP
Claims
What is claimed is:
1. A power conversion system comprising: a first voltage source; a
second voltage source; a multiple-phase alternating current motor;
a switch section configured to produce an output pulse based on
first and second output voltages of the first and second voltage
sources, respectively, to drive the multiple-phase alternating
current motor; and a control unit configured to control the switch
section including a torque computing section configured to compute
a motor current command value and a motor voltage command value
that satisfy a motor torque command value, an output voltage
command value computing section configured to compute first and
second output voltage command values for the first and second
voltage sources, respectively, that satisfy the motor current
command value, the motor voltage command value and a target charged
power that is set based on conditions of the first and second
voltage sources, and a PWM pulse generating section configured to
generate a PWM pulse for driving the switch section based on the
first and second output voltage command values, the output voltage
command value computing section of the control unit being further
configured to compute the first and second output voltage command
values based on a first output voltage command vector and a second
output voltage command vector when the first voltage source is to
be charged and the second voltage source is to be discharged, the
first output voltage command vector corresponding to the first
output voltage command value of the first voltage source satisfying
the target charged power, the second output voltage command vector
corresponding to the second output voltage command value of the
second voltage source, the first and second output voltage command
vectors being determined so that a resultant vector of the first
and second output voltage command vectors is coincident with a
motor voltage command vector corresponding to the motor voltage
command value, and a motor current command vector corresponding to
the motor current command value is positioned within an included
angle formed between the second output voltage command vector and a
negative vector of the first output voltage command vector.
2. The power conversion system recited in claim 1, wherein the
output voltage command value computing section is configured to
compute the first and second output voltage command values based on
the first and second output voltage command vectors corresponding
to when a sum of magnitudes of the first and second output voltage
command vectors is at a minimum value.
3. The power conversion system recited in claim 1, wherein the
output voltage command value computing section is configured to
compute the first and second output voltage command values such
that a sum of modulation ratios calculated based on the first and
second output voltage command values of the first and second
voltage sources and the output voltages of the first and second
voltage sources is minimized.
4. The power conversion system recited in claim 3, wherein the
output voltage command value computing section is configured to
compute the first and second output voltage command values such
that a d-q ratio of the motor current command vector equals a d-q
ratio of one of the second output voltage command vector and the
negative vector of the first output voltage command vector
corresponding to one of the first and second voltage sources having
a smaller voltage value.
5. The power conversion system recited in claim 1, wherein the
output voltage command value computing section is further
configured to calculate a revision voltage command value based on
the motor current command value, the motor voltage command value,
and the target charged power by using the following equations:
.times..times..times..times..times..times..times. ##EQU00010##
.times..times..times. ##EQU00010.2## wherein values vq_0* and vd_0*
correspond to the revision voltage command value, values id* and
iq* correspond to the motor current command value, values vd* and
vq* correspond to the motor voltage command value, and a value Pb*
corresponds to the target charged power, and to calculate the first
and second output voltage command values of the first and second
voltage sources based on the revision voltage command values by
using the following equations: vd.sub.--a*=vd*+vd.sub.--0*
vq.sub.--a*=vq*+vq.sub.--0* vd.sub.--b*=-vd.sub.--0*
vq.sub.--b*=-vq.sub.--0* wherein values vd_a*, vq_a* correspond to
the second output voltage command value of the second voltage
source and values vd_b* and vq_b* correspond to the first output
voltage command value of the first voltage source when the first
voltage source is to be charged and the second voltage source is to
be discharged.
6. The power conversion system recited in claim 1, wherein the
torque computing section is configured to compute the motor current
command value such that the motor current command vector is larger
than a minimum current command vector that satisfies the motor
torque command value and the target charged power.
7. The power conversion system recited in claim 1, wherein the
control unit further including a minimum distributed power
computing section configured to compute a minimum distributed
power, and a comparing section configured to compare magnitudes of
the minimum distributed power and the target charged power, and the
controller is further configured to change control executed in the
torque computing section and the output voltage command value
computing section based on a result of comparison obtained in the
comparing section.
8. The power conversion system recited in claim 7, wherein the
minimum distributed power computing section is configured to
compute the minimum distributed power based on a motor rotational
speed, the motor torque command value, and the first and second
output voltages of the first and second voltage sources.
9. A power conversion system comprising: a first voltage source; a
second voltage source; a multiple-phase alternating current motor;
a switch section configured to produce an output pulse based on
first and second output voltages of the first and second voltage
sources, respectively, to drive the multiple-phase alternating
current motor; and a control unit configured to control the switch
section including a torque computing section configured to compute
a motor current command value and a motor voltage command value
that satisfy a motor torque command value, an output voltage
command value computing section configured to compute first and
second output voltage command values for the first and second
voltage sources, respectively, that satisfy the motor current
command value, the motor voltage command value and a target charged
power that is set based on conditions of the first and second
voltage sources, and a PWM pulse generating section configured to
generate a PWM pulse for driving the switch section based on the
first and second output voltage command values, the output voltage
command value computing section of the control unit being further
configured to compute the output voltage command values, when the
first voltage source is to be charged and the second voltage source
is to be discharged, such that an electric power calculated based
on a motor current command waveform corresponding to the motor
current command value and a first output voltage command waveform
corresponding to the first voltage source satisfies the target
charged power, and a resultant voltage waveform of the first output
voltage command waveform corresponding to the first voltage source
and a second output voltage command waveform corresponding to the
second voltage source is coincident with a motor voltage command
waveform corresponding to the motor voltage command value, and a
location point of a positive peak of the motor current command
waveform is positioned within time interval ranging from a location
point of a negative peak of the first output voltage command
waveform to a location point of a positive peak of the second
output voltage command waveform existing within one period of the
motor current command waveform.
10. The power conversion system recited in claim 9, wherein the
output voltage command computing section is configured to compute
the output voltage command values such that a sum of an amplitude
of the first output voltage command waveform and an amplitude of
the second output voltage command waveform is minimized.
11. The power conversion system recited in claim 9, wherein the
output voltage command computing section is further configured to
synchronize a phase of the second output voltage command waveform
and a phase of the motor current command waveform with each other
when the first output voltage of the first voltage source is larger
than the second output voltage of the second voltage source, and to
shift the first output voltage command waveform and the motor
current command waveform to be out of phase with each other by
one-half of a period when the first output voltage of the first
voltage source is smaller than the second output voltage of the
second voltage source.
12. A power conversion control method comprising: outputting a
first output voltage by a first voltage source; outputting a second
output voltage by a second voltage source; driving a multiple-phase
alternating current motor by using at least one of the first and
second output voltages by producing an output pulse based on the
first and second output voltages of the first and second voltage
sources, respectively; and controlling the output pulse for driving
the multiple-phase alternating current motor by computing a motor
current command value and a motor voltage command value that
satisfy a motor torque command value, computing first and second
output voltage command values for the first and second voltage
sources, respectively, that satisfy the motor current command
value, the motor voltage command value and a target charged power
that is set based on conditions of the first and second voltage
sources, and generating a PWM pulse for producing the output pulse
based on the first and second output voltage command values, the
computing of the first and second output voltage command values
including computing the first and second output voltage command
values based on a first output voltage command vector and a second
output voltage command vector when the first voltage source is to
be charged and the second voltage source is to be discharged, the
first output voltage command vector corresponding to the first
output voltage command value of the first voltage source satisfying
the target charged power, the second output voltage command vector
corresponding to the second output voltage command value of the
second voltage source, the first and second output voltage command
vectors being determined so that a resultant vector of the first
and second output voltage command vectors is coincident with a
motor voltage command vector corresponding to the motor voltage
command value, and a motor current command vector corresponding to
the motor current command value is positioned within an included
angle formed between the second output voltage command vector and a
negative vector of the first output voltage command vector.
13. A power conversion control method comprising: outputting a
first output voltage by a first voltage source; outputting a second
output voltage by a second voltage source; driving a multiple-phase
alternating current motor by using at least one of the first and
second output voltages by producing an output pulse based on the
first and second output voltages of the first and second voltage
sources, respectively; and controlling the output pulse for driving
the multiple-phase alternating current motor by computing a motor
current command value and a motor voltage command value that
satisfy a motor torque command value, computing first and second
output voltage command values for the first and second voltage
sources, respectively, that satisfy the motor current command
value, the motor voltage command value and a target charged power
that is set based on conditions of the first and second voltage
sources, and generating a PWM pulse for producing the output pulse
based on the first and second output voltage command values, the
computing of the first and second output voltage command values
including computing the output voltage command values, when the
first voltage source is to be charged and the second voltage source
is to be discharged, such that an electric power calculated based
on a motor current command waveform corresponding to the motor
current command value and a first output voltage command waveform
corresponding to the first voltage source satisfies the target
charged power, and a resultant voltage waveform of the first output
voltage command waveform and a second output voltage command
waveform corresponding to the second voltage source is coincident
with a motor voltage command waveform corresponding to the motor
voltage command value, and a location point of a positive peak of
the motor current command waveform is positioned within time
interval ranging from a location point of a negative peak of the
first output voltage command waveform to a location point of a
positive peak of the second output voltage command waveform
existing within one period of the motor current command waveform.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims priority to Japanese Patent Application
Nos. 2006-311857 filed on Nov. 17, 2006 and 2007-263365 filed on
Oct. 9, 2007. The entire disclosures of Japanese Patent Application
Nos. 2006-311857 and 2007-263365 are hereby incorporated herein by
reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a power conversion system and a
power conversion control method.
2. Background Information
Japanese Laid-Open Patent Application Publication No. 2006-33956
discloses an example of a known motor drive system control
apparatus that uses a plurality of power sources that supply
electric power to an electric motor and that controls the electric
power supplied from each of the power sources to a desired value.
With the control apparatus disclosed in this reference, a voltage
command value applied to the motor is divided according to the
ratio of the distribution target values of the electric power
outputted from the power sources to produce a second voltage
command value group.
In view of the above, it will be apparent to those skilled in the
art from this disclosure that there exists a need for an improved
power conversion system and power conversion control method. This
invention addresses this need in the art as well as other needs,
which will become apparent to those skilled in the art from this
disclosure.
SUMMARY OF THE INVENTION
In the motor drive system control apparatus disclosed in the above
mentioned reference, the voltage command value applied to the motor
is divided into portions in accordance with the ratio indicated by
the electric target power distribution values so as to produce a
second voltage command value group. Consequently, particularly when
power is transferred among the power sources, the power factors of
the voltages outputted from the power sources will be poor if the
power factors of the current and voltage supplied to the motor are
poor. Under such conditions, a larger voltage is required in order
to supply a given current, and thus, the efficiency declines.
Therefore, one object of the present invention is to provide a
control method for a low-loss electric power converter that can
control the electric power supplied from each of a plurality of
power sources to a desired value and accomplish transferring of
power among the power sources with a high degree of efficiency.
In order to achieve the above object of the present invention, a
power conversion system includes a first voltage source, a second
voltage source, a multiple-phase alternating current motor, a
switch section and a control unit. The switch section is configured
to produce an output pulse based on first and second output
voltages of the first and second voltage sources, respectively, to
drive the multiple-phase alternating current motor. The control
unit is configured to control the switch section. The control unit
includes a torque computing section, an output voltage command
value computing section, and a PWM pulse generating section. The
torque computing section is configured to compute a motor current
command value and a motor voltage command value that satisfy a
motor torque command value. The output voltage command value
computing section is configured to compute first and second output
voltage command values for the first and second voltage sources,
respectively, that satisfy the motor current command value, the
motor voltage command value and a target charged power that is set
based on conditions of the first and second voltage sources. The
PWM pulse generating section is configured to generate a PWM pulse
for driving the switch section based on the first and second output
voltage command values. The output voltage command value computing
section of the control unit is further configured to compute the
first and second output voltage command values based on a first
output voltage command vector and a second output voltage command
vector when the first voltage source is to be charged and the
second voltage source is to be discharged. The first output voltage
command vector corresponds to the first output voltage command
value of the first voltage source satisfying the target charged
power. The second output voltage command vector corresponds to the
second output voltage command value of the second voltage source.
The first and second output voltage command vectors are determined
so that a resultant vector of the first and second output voltage
command vectors is coincident with a motor voltage command vector
corresponding to the motor voltage command value, and a motor
current command vector corresponding to the motor current command
value is positioned within an included angle formed between the
second output voltage command vector and a negative vector of the
first output voltage command vector.
These and other objects, features, aspects and advantages of the
present invention will become apparent to those skilled in the art
from the following detailed description, which, taken in
conjunction with the annexed drawings, discloses preferred
embodiments of the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
Referring now to the attached drawings which form a part of this
original disclosure:
FIG. 1 is a circuit diagram of a power converter in accordance with
a first embodiment of the present invention;
FIG. 2 is a functional block diagram of a power conversion control
system in accordance with the first embodiment of the present
invention;
FIG. 3 is a functional block diagram of a current/power control
device in accordance with the first embodiment of the present
invention;
FIG. 4 is a flowchart for a revision voltage control executed by
the power conversion control system in accordance with the first
embodiment of the present invention;
FIG. 5 is a vector diagram illustrating the relationships of output
voltage command values and current command values of the power
sources in the first embodiment of the present invention;
FIG. 6 is a schematic diagram illustrating examples of the
waveforms of the motor current and the output voltages of the power
sources in accordance with the first embodiment of the present
invention;
FIG. 7 is a schematic diagram illustrating examples of the
waveforms of the motor current and the output voltages of the power
sources in the case of a comparative example of a power conversion
system;
FIG. 8 is a flowchart explaining the revision control of the
modulation ratio executed by the power conversion control system in
accordance with the first embodiment of the present invention;
FIG. 9 is a schematic diagram illustrating the relationships of a
revision modulation ratio, a modulation ratio, and the triangular
waveform in accordance with the first embodiment of the present
invention;
FIG. 10 is a schematic diagram illustrating a triangular waveform
used by a PWM pulse generating device in accordance with the first
embodiment of the present invention;
FIG. 11 is a partial schematic view of the circuit diagram
illustrated in FIG. 1 showing only the circuit corresponding to the
U-phase in accordance with the first embodiment of the present
invention;
FIG. 12 is a schematic diagram illustrating how the pulse signals A
and E are generated by comparing with the triangular waveform in
accordance with the first embodiment of the present invention;
FIG. 13 is a schematic diagram illustrating how the pulse signals D
and C are generated by comparing with the triangular waveform in
accordance with the first embodiment of the present invention;
FIG. 14 is a schematic diagram illustrating an example of pulses
generated with dead times being added in-between in accordance with
the first embodiment of the present invention;
FIG. 15 is a functional block diagram illustrating a power
conversion control system in accordance with a second embodiment of
the present invention;
FIG. 16 is a functional block diagram illustrating a current/power
control device in accordance with the second embodiment of the
present invention;
FIG. 17 is a schematic diagram illustrating the relationships of
output voltage command values and current command values of the
power sources in accordance with the second embodiment of the
present invention;
FIG. 18 is a schematic diagram illustrating the relationships of
the output voltage command values and the current command values of
the power sources in accordance with the second embodiment of the
present invention;
FIG. 19 is a schematic diagram illustrating the relationships of
the motor current and the output voltage command values of the
power sources in accordance with the second embodiment of the
present invention;
FIG. 20 is a schematic diagram illustrating the relationships of
the motor current and the output voltage command values of the
power sources in accordance with the second embodiment of the
present invention; and
FIG. 21 is a flowchart for a revision voltage control executed by
the power conversion control system in accordance with a third
embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Selected embodiments of the present invention will now be explained
with reference to the drawings. It will be apparent to those
skilled in the art from this disclosure that the following
descriptions of the embodiments of the present invention are
provided for illustration only and not for the purpose of limiting
the invention as defined by the appended claims and their
equivalents.
FIG. 1 is a circuit diagram of a power converter 30 (switching
section) used in a power conversion control system in accordance
with the first embodiment of the present invention. As shown in
FIG. 1, the power converter 30 is electrically connected between a
plurality of power sources 10a and 10b (first and second voltage
sources) and a motor 20. The motor 20 is preferably a well-known
three-phase AC motor. More specifically, a negative electrode of
the power source 10a and a negative electrode of the power source
10b are connected to a common negative bus bar 15. A positive
electrode of the power source 10a is connected to a positive
electrode bus bar 14 and a positive electrode of the power source
10b is connected to a positive electrode bus bar 16. In the first
embodiment, the power source 10b is, for example, a well-known
secondary battery that can be selectively charged and discharged,
and the power source 10a is, for example, a well-known fuel cell
that can be discharged. The present invention is not limited to
this arrangement, however, and it is acceptable for the power
source 10a to be a secondary battery. The first embodiment of the
present invention will be explained chiefly regarding a case in
which the power source 10b is charged with electric power from the
power source 10a (i.e., the electric power is transferred between
the power sources 10a and 10b). Although the illustrated
embodiments are explained using an example where the power source
10b is charged and the power source 10a is discharged (i.e., the
power source 10b corresponds to the first voltage source to be
charged and the power source 10a corresponds to the second voltage
source to be discharged in the present invention), it will be
apparent to those skilled in the art from this disclosure that the
charging/discharging arrangement of the power sources 10a and 10b
are not limited to the arrangements described in the illustrated
embodiments. In other words, since the power sources 10a and 10b
are both capable of charging and discharging electricity, either
one of the power sources 10a and 10b can constitute the first
voltage source to be charged in the present invention as long as
the other one of the power sources 10a and 10b constitutes the
second voltage source to be discharged.
As shown in FIG. 1, the power converter 30 includes component sets
comprising semiconductor switches 107a, 108a and 109a and diodes
107b, 108b and 109b that are connected between the common negative
bus bar 15 and the terminal for each phase of the motor 20,
similarly to a lower arm of a conventional inverter. A plurality of
semiconductor switches 101a/101b, 102a/102b and 103a/103b arranged
to control current flow in both directions is connected between the
positive electrode bus bar 14 of the power source 10a and the
terminal for each phase of the motor 20. A plurality of
semiconductor switches 104a/104b, 105a/105b and 106a/106b arranged
to control current flow in both directions is connected between the
positive electrode bus bar 16 of the power source 10b and the
terminal for each phase of the motor 20. As shown in FIG. 1, a
smoothing capacitor 12 is provided between the positive electrode
bus bar 14 of the power source 10a and the common negative
electrode bus bar 15, and a smoothing capacitor 13 is provided
between the positive electrode bus bar 16 of the power source 10b
and the common negative electrode bus bar 15.
The power converter 30 is a DC-AC power converting device
configured and arranged to produce a voltage to be applied to the
motor 20 based on the electric potentials of the common negative
electrode bus bar 15, the positive electrode bus bar 14 of the
power source 10a, and the positive electrode bus bar 16 of the
power source 10b. The semiconductor switches provided with respect
to each of the phases U, V, and W of the motor 20 form three switch
groups 30U, 30V and 30W, respectively. The switch groups 30U, 30V
and 30W serve as switching device that produces voltages to be
supplied to the phases of the motor 20. More specifically, the
required voltage is supplied to the motor 20 by selectively
connecting one of these electric potentials at time and varying the
time ratio at which the selected electric potential is connected by
controlling the switch groups 30U, 30V and 30W.
Referring now to FIG. 2, the power conversion control system
provided with the power converter 30 illustrated in FIG. 1 will be
explained in accordance with the first embodiment of the present
invention. As shown in FIG. 2, in the power conversion control
system in accordance with the first embodiment, the power converter
30 is operatively coupled to a controller 40 (control unit).
The controller 40 preferably includes a microcomputer with a power
conversion control program that controls the command values for the
power sources 10a and 10b as discussed below. The controller 40 can
also include other conventional components such as an input
interface circuit, an output interface circuit, and storage devices
such as a ROM (Read Only Memory) device and a RAM (Random Access
Memory) device. The memory circuit stores processing results and
control programs that are run by the processor circuit. The
controller 40 is operatively coupled to the various components in a
conventional manner. The internal RAM of the controller 40 stores
statuses of operational flags and various control data. The
internal ROM of the controller 40 stores the maps and data for
various operations. The controller 40 is capable of selectively
controlling any of the components of the control system in
accordance with the control program. It will be apparent to those
skilled in the art from this disclosure that the precise structure
and algorithms for the controller 40 can be any combination of
hardware and software that will carry out the functions of the
present invention. In other words, "means plus function" clauses as
utilized in the specification and claims should include any
structure or hardware and/or algorithm or software that can be
utilized to carry out the function of the "means plus function"
clause. The controller 40 constitutes a torque computing section
including a torque control section 42 and a current control section
43a; an output voltage command value computing section including a
revision voltage control section 43b, a pair of multipliers 43c1
and 43c2, a pair of adders 43d1 and 43d2, and a pair of subtractors
43e1 and 43e2; a PWM pulse generating section including a
modulation ratio computing section 45, a modulation ratio revising
section 46, and a PWM pulse generating section 47; a minimum
distributed power computing section and a comparing section
including a comparator 41 of the present invention. The constituent
features of the controller 40 will now be explained with reference
to FIG. 2. The controller 40 includes the comparator 41, the torque
control section 42, a current/power control section 43, the
modulation ratio computing section 45, the modulation ratio
revising section 46, the PWM pulse generating section 47, and a
three-phase/dq converting section 48.
The comparator 41 is configured to receive a torque command Te*, a
motor rotational speed .omega., the voltage Vdc_a of the power
source 10a and the voltage Vdc_b of the power source 10b from an
external source of the controller 40 and to produce a minimum
electric power command value Pmin (minimum distributed power)
indicating the minimum electric power that can be received with
distributed power control alone. In other words, the minimum
electric power command value Pmin corresponds to a minimum electric
power value distributed to the power source 10a or 10b according to
power distribution control alone. The minimum electric power
command value Pmin is a value lying within such a range that
neither of the power source modulation ratios produced by the
distributed power control exceeds 1 and is a value that can be
received at a current value that allows the motor 20 to operate
with good efficiency. The comparator 41 is also configured to
receive an electric power command value Pb* of the power source
10b. The electric power command value Pb* corresponds to a target
charged power that is determined based on conditions of the power
sources 10a and 10b and indicates the target power distributed
between the power sources 10a and 10b. The minimum power command
value Pmin and the electric power command value Pb* of the power
source 10b are compared in the comparator 41 to produce a
comparison result Pcmpa*. The comparator 41 is configured to output
the value 0 when the electric power command value Pb* is larger
than the minimum power command value Pmin, and to output the value
1 when the electric power command value Pb* is smaller than the
minimum power command value Pmin.
Since the minimum electric power command value Pmin is a command
value for the side that receives the electric power, the minimum
electric power command value Pmin is represented as a negative
value. Thus, the minimum electric power command value Pmin
indicates the maximum value in the negative direction. When the
result of the comparison of the minimum electric power command
value Pmin and the electric power command value Pb* indicates that
the electric power command value Pb* is larger than the minimum
electric power command value Pmin, the electric power command value
Pb* is on a positive side of the minimum electric power command
value Pmin and the amount of regenerative charging power demanded
is smaller than the amount of regenerative charging power that can
be obtained with distributed power control. On the other hand, if
the electric power command value Pb* is smaller than the minimum
electric power command value Pmin, then the electric power command
value Pb* is on a negative side of the minimum electric power
command value Pmin and the amount of regenerative charging power
demanded is larger than the amount of regenerative charging power
that can be obtained with distributed power control.
The torque control section 42 is configured to compute a d-axis
current command value id* of the AC motor 20, a q-axis current
command value iq* of the AC motor 20, and a target power
distribution value rto_pa based on the comparison result Pcmpa* and
the torque command Te*, the motor rotational speed .omega., and the
electric power command value Pb* of the power source 10b obtained
from an external source of the controller 40. The torque control
section 42 is configured to refer to a preset four-dimensional map
having axes for the four factors (i.e., the torque command Te*, the
motor rotational speed .omega., the electric power command value
Pb*, and the comparison result Pcmpa*) and to output the command
values id* and iq* and the target power distribution value rto_pa.
When the four dimensional map is prepared, it is still effective
even if the command value id* for the d-axis current of the AC
motor 20 and the command value iq* for the q-axis current of the AC
motor 20 are minimum and d-axis and q-axis revision voltage values
vd_0* and vq_0* are maximum. However, in order to reduce the
amplitudes of the d-axis and q-axis revision voltage values vd_0*
and vq_0*, setting the d-axis current command value id* of the AC
motor 20 and the q-axis current command value iq* of the AC motor
to larger values is more effective from the perspective of
suppressing current ripple and reducing copper loss (ohmic loss) of
the motor because higher harmonic components are suppressed. In
other words, the torque control section 42 is preferably configured
to compute the motor current command value (id* and iq*) so that a
motor current command vector corresponding to the motor current
command value (id* and iq*) is larger than a minimum current
command value that satisfies the motor torque command value (torque
command Te*) and the target charged power (electric power command
value Pb*).
By producing the d-axis and q-axis current command values id* and
iq*, and the target power distribution value rto_pa as described
above, the current command value is left unchanged when the
electric power command value Pb* can be satisfied with a current
command value that results in a good motor efficiency and the
current command value is increased only when the electric power
command value Pb* cannot otherwise be satisfied. As a result,
output in accordance with the electric power command can be
accomplished while operating the motor 20 in an efficient state.
Additionally, since the amplitude of the revision voltage can be
reduced, current rippling can be reduced and the motor 20 can be
operated in a generally efficient state.
The current/power control section 43 is configured to produce the
d-axis and q-axis revision voltage values vd_0* and vq_0* and the
three-phase voltage command values vu_a*, vv_a* and vw_a* for the
power source 10a and the three-phase voltage command values vu_b*,
vv_b* and vw_b* for the power source 10b using the d-axis current
command value id*, the q-axis current command value iq*, a d-axis
current value id, a q-axis current value iq, the electric power
command value Pb* for the power source 10b, the comparison result
Pcmpa*, and the target power distribution values (rto_pa and
rto-pb) for the power supplied from the power sources 10a and 10b.
The target power distribution values rto_pa and rto_pb indicate a
ratio of the electric power of the power source 10a and the
electric power of the power source 10b corresponding to when the
comparison result Pcmpa* is 0 and satisfy the relationship shown
below. rto.sub.--pa+rto.sub.--pb=1
Consequently, if one of the electric target power distribution
values rto_pa and rto_pb is known, then the other of the electric
target power distribution values rto_pa and rto_pb can be
calculated using the above relationship.
When the comparison result Pcmpa* is 1 and the power source
outputting power is the power source 10a and the power source
receiving power is the power source 10b, the electric target power
distribution values rto_pa and rto_pb are set as shown below.
rto_pa=1 rto_pb=0
Referring now to FIG. 3, the current/power control section 43 of
the controller 40 will now be explained in detail. As shown in FIG.
3, the current/power control section 43 includes the current
control section 43a, the revision voltage control section 43b, the
multipliers 43c1 and 43c2, the adders 43d1 and 43d2, the
subtractors 43e1 and 43e2, a dq/three-phase converter 43f and a
dq/three-phase converter 43g.
The current control section 43a is configured to execute PI
feedback control and to output a d-axis voltage command value vd*
and a q-axis voltage command value vq* such that the current values
id and iq follow the current command values id* and iq*. The
current values id and iq are calculated by the three-phase/dq
converting section 48 shown in FIG. 2 based on the U-phase current
iu and the V-phase current iv.
The revision voltage control section 43b is configured to calculate
the d-axis and q-axis revision voltage values vd_0* and vq_0* based
on the comparison result Pcmpa* and the torque command value Te*,
the motor rotational speed .omega., and the electric power command
value Pb* of the power source 10b received from an external source
of the controller 40. The method of calculating the d-axis and
q-axis revision voltage values vd_0* and vq_0* will be explained in
more detail later.
Assuming the power source that will output electric power is the
power source 10a, the d-axis voltage command value vd* and the
q-axis voltage command value vq* outputted from the current control
section 43a are each multiplied by the distribution target value
rto_pa at the multipliers 43c1 and 43c2 so as to calculate the
d-axis and q-axis voltage command values vd_a and vq_a for the
power source 10a. vd.sub.--a=vd*.times.rto.sub.--pa
vq.sub.--a=vq*.times.rto.sub.--pa
The d-axis and q-axis revision voltage values vd_0* and vq_0*
outputted from the revision voltage control section 43b are added
to the d-axis and q-axis voltage command values vd_a and vq_a of
the power source 10a, respectively, by the adders 43d1 and 43d2 to
obtain a final d-axis voltage command value vd_a* and a final
q-axis voltage command value vq_a* for the power source 10a.
vd.sub.--a*=vd.sub.--a+vd.sub.--0*
vq.sub.--a*=vq.sub.--a+vq.sub.--0*
On the other hand, a final d-axis voltage command value vd_b* and a
final q-axis voltage command value vq_b* of the power source 10b
that will receive electric power are calculated by subtracting the
final d-axis and q-axis voltage command values vd_a* and vq_a* of
the power source 10a from the d-axis and q_axis voltage command
values vd* and vq* outputted from the current control section 43a,
respectively, using the subtractors 43e1 and 43e2.
vd.sub.--b*=vd*-vd.sub.--a* vq.sub.--b*=vq*-vq.sub.--a*
The dq/three-phase converters 43f and 43g are dq/three-phase
converting devices configured to convert d-axis voltage and a
q-axis voltage into a three-phase voltage command. In other words,
the dq/three-phase converter 43f serves to convert the final d-axis
and q-axis voltage command values vd_a* and vq_a* for the power
source 10a into the three-phase voltage command values vu_a*, vv_a*
and vw_a*. Likewise, the dq/three-phase converter 43g serves to
convert the final d-axis and q-axis voltage command values vd_b*
and vq_b* for the power source 10b into the three-phase voltage
command values vu_b*, vv_b* and vw_b*.
While the preceding paragraphs explain the overall operation of the
current/power control section 43, the calculation of the d-axis and
q-axis revision voltage values vd_0* and vq_0* will now be
explained with reference to FIGS. 4 and 5. FIG. 4 is a basic
flowchart for obtaining the d-axis and q-axis revision voltage
values vd_0* and vq_0* executed by the revision voltage control
section 43b.
As shown in FIG. 4, in the first embodiment of the present
invention, the d-axis and q-axis revision voltage values vd_0* and
vq_0* are set to 0 (step S12) when the value of the comparison
result Pcmpa* is 0 (No in step S10). On the other hand, when the
comparison result Pcmpa* is 1 (Yes in step S10), the values vd_0*
and vq_0* are found using the preset five-dimensional map having
axes corresponding to vd*, vq*, id*, iq*, and Pb* (step S11).
The method of setting the d-axis and q-axis revision voltage values
vd_0* and vq_0* will now be explained with reference to the vector
diagram shown in FIG. 5. FIG. 5 shows a first output voltage
command vector or first vector (indicated as Vdq_b*) corresponding
to the output voltage command value Vdq_b* of the power source 10b
and a second output voltage command vector or second vector
(indicated as Vdq_a*) corresponding to the output voltage command
value Vdq_a* of the power source 10a. The output voltage command
value Vdq_a* of the power source 10a (the second vector) represents
the final d-axis and q-axis voltage command values vd_a* and vq_a*
of the power source 10a to which the d-axis and q-axis revision
voltage values vd_0* and vq_0*, which were determined by referring
to the preset five-dimensional map, have been included. The output
voltage command value Vdq_b* of the power source 10b (the first
vector) represents the final d-axis and q-axis voltage command
values vd_b* and vq_b* of the power source 10b obtained based on
the final d-axis and q-axis voltage command values vd_a* and vq_a*
of the power source 10a. FIG. 5 also shows a motor current command
vector (indicated as Idq*) corresponding to the motor current
command value Idq* and a motor voltage command vector (indicated as
Vdq*) corresponding to the motor voltage command value Vdq*. The
motor current command value Idq* includes the d-axis and q-axis
current command values id* and iq*. The motor voltage command value
Vdq* includes the d-axis and q-axis voltage command values vd* and
vq*.
FIG. 5 shows an example of the first vector (Vdq_b*) and the second
vector (Vdq_a*) that satisfy the electric power command value Pb*.
A plurality of points 1a to 6a indicated with square dots and a
plurality of points 1b to 6b indicated with circular dots in FIG. 5
represent the values that the first vector (Vdq_b*) and the second
vector (Vdq_a*) can have in order to satisfy the electric power
command value Pb* (the target charged power). Moreover, a plurality
of points 1b' to 6b' indicated with diamond-shape dots in FIG. 5
represents the values that correspond to the negative vectors of
the values 1b to 6b. As will be explained in more detail later,
since the sum of the second vector (Vdq_a*) and the first vector
(Vdq_b*) is always required to be equal to the motor voltage
command vector (Vdq*), the values that the second vector (Vdq_a*)
and the first vector (Vdq_b*) can have are correlated with each
other (i.e., 1a-1b (1b'), 2a-2b (2b'), 3a-3b (3b'), . . . ). Of
course, the values that the second vector (Vdq_a*) and the first
vector (Vdq_b*) can have vary depending on the value of the
electric power command value Pb* (the target charged power). As
mentioned in the explanation of the overall operation of the
current/power control section 43, the d-axis and q-axis revision
voltage values vd_0* and vq_0* are values that are added to the
d-axis and q-axis voltage command values vd_a and vq_a of the power
source 10a in order to obtain the final d-axis and q-axis voltage
command values vd_a* and vq_a* of the power source 10a.
In the first embodiment, the following conditions are satisfied
when the d-axis and q-axis revision voltage values vd_0* and vq_0*
are obtained by using the five-dimensional map: the resultant
vector of the second vector (Vdq_a*) and the first vector (Vdq_b*)
is coincident with the motor voltage command vector (Vdq*), and the
motor current command vector (Idq*) lies within an included angle
formed between the second vector (Vdq_a*) and a negative vector
(-Vdq_b*) of the first vector (Vdq_b*). The negative vector
(-Vdq_b*) of the first vector (Vdq_b*) is a vector having the same
point of origin and the same magnitude as the first vector (Vdq_b*)
but directed in a 180-degree opposite direction from the first
vector (Vdq_b*). The included angle is the smaller angle formed
between the second vector (Vdq_a*) and the negative vector
(-Vdq_b*) of the first vector (Vdq_b*), and is indicated as
.theta.1 in FIG. 5. More specifically, the d-axis and q-axis
revision voltage values vd_0* and vq_0* are determined so that the
motor current command vector (Idq*) is equal to a value including a
value equal to the second vector (Vdq_a*), a value equal to the
negative vector (-Vdq_b*) of the first vector (Vdq_b*), and any
value falls within the narrow-angle formed between the second
vector (Vdq_a*) and the negative vector (-Vdq_b*) of the first
vector (Vdq_b*). After satisfying the aforementioned conditions,
the second vector (Vdq_a*) and the first vector (Vdq_b*), with
which the sum of the magnitudes of the second vector (Vdq_a*) and
the first vector (Vdq_b*) is minimized, are calculated. Then, the
difference between the second vector (Vdq_a*) and the motor voltage
command vector (Vdq*) is calculated as a revision voltage vector
corresponding to a revision voltage command value vdq_0*. The d
component and q component of the revision voltage vector (vdq_0*)
are outputted as the d-axis and q-axis revision voltage values
vd_0* and vq_0*.
FIG. 6 illustrates the waveforms corresponding to the motor current
command value Idq* (motor current command waveform), the motor
voltage command value Vdq* (motor voltage command waveform), the
output voltage command value Vdq_a* of the power source 10a (second
output voltage command waveform), and the output voltage command
value Vdq_b of the power source 10b (first output voltage command
waveform) in accordance with the first embodiment of the present
invention. The horizontal axis indicates phase (time), and the
vertical axis indicates amplitude of voltage or current. The
waveforms illustrated in FIG. 6 correspond to the vectors
illustrated in the vector diagram of FIG. 5.
In order to facilitate the understanding of the present invention,
the waveforms of the motor current command value, Idq*, the motor
voltage command value Vdq*, the output voltage command value Vdq_a*
of the power source 10a, and the output voltage command value
Vdq_b* of the power source 10b obtained with a comparative example
of a distributed power control are shown in FIG. 7. In FIG. 7,
since the positive peak of the motor voltage command waveform
(Vdq*), the positive peak of the output voltage command waveform
(Vdq_a*) of the output source 10a, and the negative peak (valley)
of the output voltage command waveform (Vdq_b*) of the output
source 10b are aligned at time T, the power factor of the motor
current command waveform (Idq*) and the motor voltage command
waveform (Vdq*) is equal to the power factor of the motor current
command waveform (Idq*) and the output voltage command waveform
(Vdq_a*) of the output source 10a, and the power factor of the
motor current command waveform (Idq*) and the output voltage
command waveform (Vdq_b*) of the output source 10b. On the other
hand, in the first embodiment of the present invention as shown in
FIG. 6, an electric power that is calculated based on the motor
current command waveform (Idq*) corresponding to the d-axis and
q-axis motor current command values id* and iq* and the output
voltage command waveform (Vdq_b*) of the power source 10b (which is
the power source to be charged) satisfies the electric power
command value Pb* of the power source 10b (the target charged
power). Moreover, a resultant voltage waveform of the output
voltage command waveform (Vdq_b*) of the power source 10b and the
output voltage command waveform (Vdq_a*) of the power source 10a
(which is the power source to be discharged) is coincident with the
motor voltage command waveform (Vdq*) corresponding to the d-axis
and q-axis motor voltage command values vd* and vq*. Additionally,
the output voltage command waveform (Vdq_a*) of the power source
10a and the output voltage command waveform (Vdq_b*) of the power
source 10b are generated such that the positive peak of the motor
current command waveform (Idq*), which occurs at time Ti, is
sandwiched between the positive peak of the output voltage command
waveform (Vdq_a*) of the power source 10a, which occurs at time Ta,
and the negative peak (valley) of the output voltage command
waveform (Vdq_b*) of the power source 10b, which occurs at time Tb.
Thus, the distances between the positive peak of the motor current
command waveform (Idq*), the positive peak of the output voltage
command waveform (Vdq_a*) of the power source 10a, and the negative
peak (valley) of the output voltage command waveform (Vdq_b*) of
the power source 10b are smaller than those distances in the
comparative example illustrated in FIG. 7. In short, the power
factors of the motor current command value Idq* and of the output
voltage command values Vdq_a* of the power source 10a and the
output voltage command value Vdq_b* of the power source 10b are
both improved in comparison with the comparative technology shown
in FIG. 7. As shown in FIG. 6, in the first embodiment of the
present invention, time Ti occurs within the time interval between
time Ta and time Tb. In this explanation, the expressions
"sandwiched between" and "positioned (occurring) within the time
interval" include cases in which the peak of either the output
voltage command waveform (Vdq_a*) of the power source 10a or the
output voltage command waveform (Vdq_b*) of the power source 10b
coincides with the peak of the motor current command waveform
(Idq*).
Referring back to FIG. 2, the modulation ratio computing section 45
is configured to receive the voltage Vdc_a of the power source 10a
and the voltage Vdc_b of the power source 10b as input and to
produce normalized voltage commands, i.e., momentary modulation
ratio commands mu_a*, mu_b*, mv_a*, mv_b*, mw_a*, and mw_b*. The
modulation ratio revising section 46 is configured to execute a
pre-processing of the momentary modulation ratio commands mu_a*,
mu_b*, mv_a*, mv_b*, mw_a*, and mw_b* to produce final momentary
modulation ratio commands mu_a_c*, mu_b_c*, mv_a_c*, mv_b_c*,
mw_a_c*, and mw_b_c* before pulse width modulation (PWM) is
executed. The PWM pulse generating section 47 is configured to
produce PWM pulses for turning the switches of the electric power
converter 30 on and off based on the final momentary modulation
ratio commands mu_a_c* mu_b_c*, mv_a_c*, mv_b_c*, mw_a_c*, and
mw_b_c*.
The modulation ratio computing section 45, the modulation ratio
revising section 46, and the PWM pulse generating section 47 will
now be described in more detail. In the following explanation, the
operation is explained with respect to the U phase only. However,
the operation is exactly the same with respect to the V phase and W
phase, as well.
Modulation Ratio Computing Section 45
The modulation ratio computing section 45 is configured to
calculate the momentary modulation ratio command mu_a* for the
power source 10a and the momentary modulation ratio command mu_b*
for the power source 10b by normalizing the U-phase voltage command
vu_a* for the power source 10a and the U-phase voltage command
vu_b* for the power source 10b with values equal to one half of the
DC voltage of each of the power sources 10a and 10b.
mu.sub.--a*=vu.sub.--a*/(Vdc.sub.--a/2)
mu.sub.--b*=vu.sub.--b*/(Vdc.sub.--b/2)
Modulation Ratio Revising Section 46
The flowchart of FIG. 8 shows the computational operations executed
by the modulation ratio revising section 46 in detail. In this
computation, the time period of the PWM cycle is distributed in
order to output the obtained modulation ratios. First, the values
ma_offset0 and mb_offset0 shown below are computed based on the
voltages Vdc_a and Vdc_b of the power sources 10a and 10b,
respectively. The value rto_pb is calculated using the equation
described previously.
.times..times..times..times..times..times..times..times..times..times.
##EQU00001##
The details will now be explained with reference to FIG. 8. In step
S20, the modulation ratio computing section 46 is configured to
compare the sizes of the voltages Vdc_a and Vdc_b of the power
sources 10a and 10b. After the comparison in step S20, the
modulation ratio computing section 46 is configured to compute a
value of a modulation ratio amplitude offset_d0 that needs to be
secured in order to output the d-axis and q-axis revision voltage
values vd_0* and vq_0*. Since the modulation ratio amplitude
offset_d0 becomes larger as the voltages Vdc_a and Vdc_b of the
power sources 10a and 10b become smaller, the sizes of the voltages
Vdc_a and Vdc_b of the power sources 10a and 10b are compared in
advance in step S20 in order to secure the required modulation
ratio amplitude.
If the value of the voltage Vdc_a of the power source 10a is not
larger than the value of the voltage Vdc_b of the power source 10b
(No in step S20), then the modulation ratio computing section 46
proceeds to step S22. In step S22, the modulation ratio computing
section 46 is configured to calculate the modulation ratio
amplitude offset_d0 using the equation (2) below.
.times..times..times..times..times..times..times..times.
##EQU00002##
On the other hand, if the value of the voltage Vdc_a of the power
source 10a is larger than the value of the voltage Vdc_b of the
power source 10b (Yes in step S20), then the modulation ratio
computing section 46 proceeds to step S21. In step S21, the
modulation ratio computing section 46 is configured to calculate
the modulation ratio amplitude offset_d0 using the equation (3)
below.
.times..times..times..times..times..times..times..times.
##EQU00003##
After calculating the modulation ratio amplitude offset_d0 in step
S21 or S22, the modulation ratio computing section 46 proceeds to
step S23. In step S23, the modulation ratio computing section 46 is
configured to compare the sizes of the value ma_offset0 and the
value mb_offset0 that are previously calculated as described above.
The modulation ratio computing section 46 is then configured to add
the modulation ration amplitude offset_d0 to the smaller one of the
values ma_offset0 and mb_offset0 in order to obtain an offset value
that will enable the modulation ratio amplitude to be
outputted.
More specifically, the values ma_offset0 and mb_offset0 have the
following relationship. ma_offset0+mb_offset0=1
Therefore, the conditional relationship ma_offset0>mboffset0 can
be expressed as follows: ma_offset0>1/2
If this condition is satisfied, i.e., if the result of step S23 is
Yes (true), then the value mb_offset0 is smaller than the value
ma_offset0, and the offset value is calculated by adding the value
mb_offset0 to the modulation ratio amplitude offset_d0 in step S24
as follows. mb_offset=mb_offset0+offset.sub.--d0
The value of mb_offset is not to exceed 1, and thus, in step S25,
the value mb_offset is passed through a limiter having 1 as the
upper limit value to obtain the output mb_offset*.
In step S26, the output mb_offset* of the limiter is used to
calculate the value ma_offset* using the equation shown below.
ma_offset*=1-mb_offset*
On the other hand, if the condition of step S23 is not satisfied,
i.e., if the result is No (false), then the value ma_offset0 is
smaller than the value mb_offset0, and the offset value is
calculated by adding the value ma_offset0 to the modulation ratio
amplitude offset_d0 in step S27 as follows.
ma_offset=ma_offset0+offset.sub.--d0
The value of ma_offset is not to exceed 1, and thus, in step S28,
the value ma_offset is passed through a limiter having 1 as the
upper limit value to obtain the output ma_offset*.
In step S29, the output ma_offset* of the limiter is used to
calculate the value mb_offset* using the equation shown below.
mb_offset*=1-ma_offset*
The momentary modulation ratio command mu_a* for the power source
10a and the momentary modulation ratio command mu_b* for the power
source 10b are revised using the offset values ma_offset* and
mb_offset* to obtain the output values (final momentary modulation
ratio commands) mu_a_c* and mu_b_c*.
mu.sub.--a.sub.--c*=mu.sub.--a*+ma_offset*-1
mu.sub.--b.sub.--c*=mu.sub.--b*+mb_offset*-1
Executing this kind of revision calculation enables sufficient time
to be secured for outputting the modulation ratio commands when a
triangular wave comparison is executed. For example, when rto_pa=1,
even though mb_offset0=0, some time for outputting a d-axis
revision voltage can be secured because mb_offset includes the
added value offset_do. The diagrams (a) and (b) of FIG. 9 show the
final momentary modulation ratio commands mu_b_c* and mb_offset in
such a case and illustrate how adding the value mb_offset to the
momentary modulation ration command mu_b* enables the triangular
wave comparison to be accomplished.
PWM Pulse Generating Section 47
The manner in which the PWM pulse generating section 47 generates
the PWM pulse will now be explained. As shown in FIG. 10, a carrier
wave for the power source 10a is a triangular carrier wave for
generating PWM pulses for driving the switches so as to output
voltage pulses from the voltage Vdc_a of the power source 10a.
Similarly, a carrier for the power source 10b is a triangular
carrier wave. These two triangular carrier waves range between an
upper limit value of +1 and a lower limit value of -1 and are 180
degrees out of phase with each other. Signals for driving the
switches of the U phase are defined as presented below based on
FIG. 11.
Signal A: a drive signal for the switch 101a serving to provide an
electrical connection for electricity flowing from the power source
10a to an output terminal.
Signal B: a drive signal for the switch 107a serving to provide an
electrical connection for electricity flowing from the output
terminal to a negative electrode.
Signal C: a drive signal for the switch 101b serving to provide an
electrical connection for electricity flowing from the output
terminal to the power source 10a.
Signal D: a drive signal for the switch 104a serving to provide an
electrical connection for electricity flowing from the power source
10b to an output terminal.
Signal E: a drive signal for the switch 104b serving to provide an
electrical connection for electricity flowing from the output
terminal to the power source 10b.
The pulse generation method used to produce the voltage pulses from
the power source 10a will now be explained. The signal A (the
switch 101a) needs to be on in order to output PWM pulses from the
voltage source 10a. When a potential difference exists between a
positive electrode of the power source 10a and a positive electrode
of the power source 10b and the condition Vdc_a>Vdc_b exists, a
current that short circuits the positive electrodes of the power
sources 10a and 10b will flow if both the signal A and the signal E
are turned on (i.e., the switch 101a and 104b are on). For example,
if the signal A is switched from on to off and the signal E is
switched from off to on simultaneously, then there will be a period
of time when both signals are on because it takes time for the
signal A to turn completely off and the on states of both switches
101a and 104b will overlap. When this occurs, a short circuit
current will flow and the amount of heat emitted from a
semiconductor switch installed along the path of the short circuit
current will increase. In order to prevent such an increase in
emitted heat, the signal A or E being turned from off to on is not
switched on until a period of time during which both of the drive
signals A and E are off elapses. Thus, the pulses are generated
using drive signals that include a short circuit prevention time
(dead time). Similarly to the addition of a dead time between the
drive signals A and E, a dead time is added between the drive
signals E and C. Moreover, in order to prevent short circuiting
between the positive electrode and the negative electrode, a dead
time is added between the drive signals A and B and the drive
signals E and B.
The method of adding a dead time to the drive signals A and E will
now be explained with reference to FIG. 12. In order to generate
drive signals having a dead time, a value mu_a_c_up* and a value
mu_a_c_down* that are offset from the value mu_a_c* by the amount
of the dead time are calculated as shown below.
mu.sub.--a.sub.--c_up*=mu.sub.--a.sub.--c*+Hd
mu.sub.--a.sub.--c_down*=mu.sub.--a.sub.--c*-Hd
The value Hd in the above equations is calculated as shown below
based on the amplitude Htr of the triangular waveform (from the
base to the apex), the period Ttr of the triangular waveform, and
the dead time Td. Hd=2Td.times.Htr/Ttr
A comparison of the carrier and the values mu_a_c*, mu_a_c_up*, and
mu_a_c_down* is executed and the states of the drive signals of the
switches A and E are determined according to the following
rules:
If mu_a_c_down*.gtoreq.the carrier for the power source 10a, then
set A=ON;
If mu_a_c_*.ltoreq.the carrier for the power source 10a, then set
A=OFF;
If mu_a_c_*.gtoreq.the carrier for the power source 10a, then set
E=OFF; and
If mu_a_c_up*.ltoreq.the carrier for the power source 10a, then set
E=ON.
By generating the drive signals in this way, a dead time Td can be
provided between A and E and short circuiting between the positive
electrodes can be prevented.
Similarly, the pulse generation method used to produce the voltage
pulses from the power source 10b involves finding the values
mu_b_c_up* and mu_b_c_down* using the following equations and
comparing to the carrier for the power source 10b. FIG. 13
illustrates the pulse generation of the signals D and C by means of
a triangular waveform comparison.
mu.sub.--b.sub.--c_up*=mu.sub.--b.sub.--c*+Hd
mu.sub.--b.sub.--c_down*=mu.sub.--b.sub.--c*-Hd
The states of the drive signals of the switches D and C are
determined according to the following rules:
If mu_b_c_down*.gtoreq.the carrier for the power source 10b, then
set D=ON;
If mu_b_c_*.ltoreq.the carrier for the power source 10b, then set
D=OFF;
If mu_b_c_*.gtoreq.the carrier for the power source 10b, then set
C=OFF; and
If mu_b_c_up*.ltoreq.the carrier for the power source 10b, then set
C=ON.
In this way, a dead time Td can be provided between the signals D
and C and short circuiting between the positive terminals can be
prevented.
The drive signal B is generated from a logical AND condition of the
generated drive signals E and C. B=E.times.C
The drive signal E includes a dead time with respect to the drive
signal A and the drive signal C includes a dead time with respect
to the drive signal D. Thus, since the drive signal B is generated
from a logical AND of the drive signals E and C, dead times can
also be generated between the drive signals B and A and between the
drive signals B and E. An example of pulses generated with dead
times in-between is shown in FIG. 14. The output voltage pulses are
generated by turning the switches of the electric power converter
on and off based on the PWM pulses generated as just described. By
taking an average of the voltage pulse produced from the voltage
Vdc_a of the power source 10a and the voltage pulse produced from
the voltage Vdc_b of the power source 10b in each cycle, a voltage
pulse that achieves the original three-phase voltage command values
vu*, vv*, and vw* is obtained.
Accordingly, in first embodiment of the present invention described
above, when the output voltage command values Vdq_a* and Vdq_b* of
the first and second power sources 10a and 10b, and the motor
current command value Idq* are expressed as vectors, the revision
voltage value vdq_0* is generated such that the motor current
command vector (Idq*) is positioned (lies) within the included
angle .theta.1 formed by the first vector (Vdq_b*) and the second
vector (Vdq_a*). As a result, the optimum output voltage command
values Vdq_a* and Vdq_b* can be selected for each of the power
sources 10a and 10b and degradation of the power factors of the
motor current command value Idq* and the output voltage command
values Vdq_a* and Vdq_b* outputted from each of the power sources
10a and 10b can be reduced.
When electric power is transferred between the power sources 10a
and 10b with the power converter 30 under low torque conditions, a
feasible method of preventing the motor torque from changing is to
increase the ineffective current Id. However, if the current Id is
simply increased (particularly when the torque is 0), then there
will be a plurality of the output voltage command values Vdq_a* and
Vdq_b* that satisfy the current Id (current command value) and the
electric power command value Pb*. Therefore, there will be a
possibility that the power factors of the motor current command
value Idq* and the output voltage command values Vdq_a* and Vdq_b*
for the power sources 10a and 10b will decline. Therefore, the
present invention is particularly effective under low torque
conditions.
Additionally, in the first embodiment of the present invention,
since the d-axis and q-axis revision voltage values vd_0* and vq_0*
are set such that the sum of the sizes of the output voltage
command values Vdq_a* and Vdq_b* for the power sources 10a and 10b
is minimized, the amplitudes of the voltages outputted from the
power sources 10a and 10b can be minimized and the generation of
ineffective power can be reduced, thereby enabling the electric
power transfer to be conducted with a high degree of
efficiency.
Thus, with the first embodiment of the present invention, electric
power transfer between the power sources 10a and 10b can be
adjusted by generating the motor current command vector (Idq*), the
first vector (Vdq_b*) and the second vector (Vdq_a*) based on the
electric power command value Pb* (the target charged power).
Although the power of the motor 20 is low when the motor torque
command Te* is low, power transfer between the power sources 10a
and 10b can be accomplished with good control precision and good
efficiency by using the motor current command vector (Idq*), the
first vector (Vdq_b*) and the second vector (Vdq_a*) according to
the first embodiment of the present invention. Furthermore, since
the motor current command vector (Idq*), the first vector (Vdq_b*)
and the second vector (Vdq_a*) are generated such that the motor
current command vector (Idq*) is located between the second vector
(Vdq_a*) and the negative vector (-Vdq_b*) of the first vector
(Vdq_b*), power transfer can be accomplished with good power
factors and good efficiency.
Second Embodiment
Referring now to FIGS. 15 to 20, a power conversion system in
accordance with a second embodiment will now be explained. In view
of the similarity between the first and second embodiments, the
parts of the second embodiment that are identical to the parts of
the first embodiment will be given the same reference numerals as
the parts of the first embodiment. Moreover, the descriptions of
the parts of the second embodiment that are identical to the parts
of the first embodiment may be omitted for the sake of brevity. The
parts of the second embodiment that differ from the parts of the
first embodiment will be indicated with a single prime (').
FIG. 15 is a functional block diagram of the power conversion
system in accordance with the second embodiment of the present
invention. As shown in FIG. 15, the power conversion system of the
second embodiment is identical to the power conversion system of
the first embodiment illustrated in FIG. 2 except for the control
executed by a current power control section 43' of the controller
40.
FIG. 16 is a functional block diagram of the current/power control
section 43' of the controller 40 in accordance with the second
embodiment. The current/power control section 43' of the second
embodiment is identical to the current/power control section 43 of
the first embodiment illustrated in FIG. 3 except for the operation
executed in a revision voltage control section 43b'. The
differences between the first and second embodiments will now be
explained with reference to FIG. 16.
The control operation executed in the revision voltage control
section 43b' of the second embodiment is basically the same as the
control operation shown in the flowchart of FIG. 4. More
specifically, the revision voltage control section 43b' is
configured to generate the d-axis and q-axis revision voltage
values vd_0* and vq_0* based on the comparison result Pcmpa*, the
voltage Vdc_a of the power source 10a, the voltage Vdc_b of the
power source 10b, the d-axis voltage command value vd*, the q-axis
voltage command value vq*, the d-axis current command value id*,
the q-axis current command value iq*, and the electric power
command value Pb* of the power source 10b.
In step S10 of FIG. 4, the revision voltage control section 43' is
configured to determine if the value of the comparison result
Pcmpa* is 0 or 1. If the value of the comparison result Pcmpa* is 0
(No in step S10), the d-axis and q-axis revision voltage values
vd_0* and vq_0* are set to 0 in step S12. If the value of the
comparison result Pcmpa* is 1 (Yes in step S11), then the values
vd_0* and vq_0* are determined using a prepared map. In the second
embodiment of the present invention, a preset seven-dimensional map
having axes corresponding to the voltage Vdc_a, the voltage Vdc_b,
the d-axis voltage command value vd*, the q-axis voltage command
value vq*, the d-axis current command value id*, the q-axis current
command value iq*, and the electric power command value Pb* of the
power source 10b is used to determine the d-axis and q-axis
revision voltage values vd_0* and vq_0* in step S11.
The seven-dimensional map used in step S11 in the second embodiment
is prepared based on the following equation (4). The d-axis and
q-axis revision voltage values vd_0* and vq_0* are set such that
the modulation ratio mu is minimized.
.times..times..times..times..times..times..times..times..times..times..ti-
mes..times..times. ##EQU00004##
The method for setting the d-axis and q-axis revision voltage
values vd_0* and vq_0* will now be explained with reference to the
vector diagrams shown in FIGS. 17 and 18. On d-q coordinates, FIGS.
17 and 18 show a first vector (indicated as Vdq_b*) corresponding
to the output voltage command value Vdq_b* of the power source 10b
and a second vector (indicated as Vdq_a*) corresponding to the
output voltage command value Vdq_a* of the power source 10a. The
output voltage command value Vdq_a* of the power source 10a (the
second vector) represents the final d-axis and q-axis voltage
command values vd_a* and vq_a* of the power source 10a to which the
d-axis and q-axis revision voltage values vd_0* and vq_0*, which
were determined by referring to the preset seven-dimensional map,
have been added. The output voltage command value Vdq_b* of the
power source 10b (the first vector) represents the final d-axis and
q-axis voltage command values vd_b* and vq_b* of the power source
10b obtained based on the final d-axis and q-axis voltage command
values vd_a* and vq_a* of the power source 10a. The vector diagrams
in FIGS. 17 and 18 also show a motor current command vector
(indicated as Idq*) corresponding to the motor current command
value Idq* and a motor voltage command vector (indicated as Vdq*)
corresponding to the motor voltage command value Vdq*. The motor
current command value Idq* includes the d-axis and q-axis current
command values id* and iq*. The motor voltage command value Vdq*
includes the d-axis and q-axis voltage command values vd* and
vq*.
In the second embodiment, the following conditions are satisfied on
FIGS. 17 and 18 when the d-axis and q-axis revision voltage values
vd_0* and vq_0* are obtained using the seven-dimensional map: the
resultant vector of the second (Vdq_a*) and the first vector
(Vdq_b*) is coincident with the motor voltage command vector
(Vdq*), and the motor current command vector (Idq*) lies (exists)
within an included angle formed between the second vector (Vdq_a*)
and a negative vector (-Vdq_b*) of the first vector (Vdq_b*). The
negative vector (-Vdq_b*) of the first vector (Vdq_b*) is a vector
having the same point of origin and the same magnitude as the first
vector (Vdq_b*) but directed in a 180-degree opposite direction
from the first vector (Vdq_b*). The included angle is the smaller
angle formed between the first vector (Vdq_a*) and the negative
vector (-Vdq_b*) of the first vector (Vdq_b*), and is indicated as
.theta.2 and .theta.3 in FIGS. 17 and 18, respectively. Upon
satisfying the aforementioned conditions, the d-axis and q-axis
revision voltage values vd_0* and vq_0* are outputted which
minimize the sum mu of the magnitudes of the normalized modulation
ratios obtained by normalizing the voltage command values of the
power supplies with the power supply voltages.
FIG. 17 is a vector diagram illustrating a case in which the
voltage of the power source 10a is lower than the voltage of the
power source 10b, the voltage command value outputted by the
voltage source 10a has been minimized, and the modulation ratio is
at a minimum. The second vector (Vdq_a*) and the first vector
(Vdq_b*) are calculated such that the motor current command vector
(Idq*) exists (lies) within the included angle .theta.2 formed
between the second vector (Vdq_a*) and the negative vector
(-Vdq_b*) of the first vector (Vdq_b*). Moreover, the d-q ratio of
the second vector (Vdq_a*) corresponding to the smaller voltage
equals the d-q ratio of the motor current command vector (Idq*).
The d-axis and q-axis revision voltage values vd_0* and vq_0* are
generated (adjusted) from the d-axis and q-axis components of a
revision voltage vector vdq_0* that is calculated as a difference
between the first vector (Vdq_a*) and the motor voltage command
vector (Vdq*).
FIG. 18 is a vector diagram illustrating a case in which the
voltage of the power source 10b is lower than the voltage of the
power source 10a, the voltage command value outputted by the
voltage source 10b has been minimized, and the modulation ratio is
at a minimum. The second vector (Vdq_a*) and the first vector
(Vdq_b*) are calculated such that the motor current command vector
(Idq*) exists (lies) within the included angle .theta.3 formed
between the second vector (Vdq_a*) and the negative vector
(-Vdq_b*) of the first vector (Vdq_b*). Moreover, the d-q ratio of
the first vector (Vdq_b*) corresponding to the smaller voltage in
this case equals the d-q ratio of the motor current command vector
(Idq*). The d-axis and q-axis revision voltage values vd_0* and
vq_0* are generated (adjusted) from the d-axis and q-axis
components of a revision voltage vector vdq_0* that is calculated
as a difference between the second vector (Vdq_a*) and the motor
voltage command vector (Vdq*). In short, the power factors of the
motor current command value Idq* and the output voltage command
value Vdq_a* for the power source 10a are best under the conditions
shown in FIG. 17. On the other hand, the power factors of the motor
current command value Idq* and the output voltage command
value--Vdq_b* for the power source 10b are best under the
conditions shown in FIG. 18.
FIGS. 19 and 20 illustrate the waveforms corresponding to the motor
current command value Idq* (motor current command waveform), the
motor voltage command value Vdq* (motor voltage command waveform),
the output voltage command value Vdq_a* of the power source 10a
(second output voltage command waveform), and the output voltage
command value Vdq_b* of the power source 10b (first output voltage
command waveform) in accordance with the first embodiment of the
present invention. The horizontal axis indicates phase (time), and
the vertical axis indicates amplitude of voltage or current.
The waveforms illustrated in FIG. 19 correspond to the vectors
illustrated in the vector diagram of FIG. 17. The waveforms
illustrated in FIG. 20 correspond to the vectors illustrated in the
vector diagram of FIG. 18. Explanations of the relationships
between Vdq_a*, Vdq_b*, Pb*, and Vdq* are omitted because they are
similar to the first embodiment explained above.
In the example shown in FIG. 19, the distances between the positive
peak of the motor current command waveform (Idq*), which occurs at
time Ti, the positive peak of the output voltage command waveform
(Vdq_a*) of the power source 10a, which occurs at time Ta, and the
negative peak (valley) of the output voltage command waveform
(Vdq_b*) of the power source 10b, which occurs at time Tb, are
smaller than in the example shown in FIG. 7, which illustrates a
comparative distributed power control technology. Additionally, the
peak of the motor current command waveform (Idq*), which occurs at
the time Ti, and the positive peak of the output voltage command
waveform (Vdq_a*) of the power source 10a, which occurs at the time
Ta, are coincident (occur at the same time). Under the conditions
of FIG. 17, control is executed such that a voltage waveform
corresponding to the sum of the output voltage command waveform
(Vdq_a*) of the power source 10a and the output voltage command
waveform (Vdq_b*) of the power source 10b is the motor voltage
command waveform (Vdq*), and the positive peak of the motor current
command waveform (Idq*) and the positive peak of the output voltage
command waveform (Vdq_a*) of the power source 10a occur
coincidentally (occur at the same time). Thus, the power factor is
improved over the comparative technology and the modulation ratio
can be minimized. The output voltage command values Vdq_a* and
Vdq_b* for the power sources 10a and 10b are computed such that a
sum of modulation ratios calculated based on the output voltage
command values Vdq_a* and Vdq_b* of the power sources 10a and 10b
and the output voltages of the power sources 10a and 10b is
minimized.
In the example shown in FIG. 20, the distances between the positive
peak of the motor current command waveform (Idq*), which occurs at
time Ti, the positive peak of the output voltage command waveform
(Vdq_a*) of the power source 10a, which occurs at time Ta, and the
negative peak (valley) of the output voltage command waveform
(Vdq_b*) of the power source 10b, which occurs at time Tb, are
smaller than in the example shown in FIG. 7, which illustrates a
comparative distributed power control technology. Additionally, the
positive peak of the motor current command waveform (Idq*) and the
negative peak (valley) of the output voltage command waveform
(Vdq_b*) of the power source 10b are coincident (occur at the same
time). Under the conditions of FIG. 18, control is executed such
that a voltage waveform corresponding to the sum of the output
voltage command waveform (Vdq_a*) of the power source 10a and the
output voltage command waveform (Vdq_b*) of the power source 10b is
the motor voltage command waveform (Vdq*), and the positive peak of
the motor current command waveform (Idq*) and the negative peak
(valley) of the output voltage command waveform (Vdq_b*) of the
power source 10b occur coincidentally (at the same time). Thus, the
power factor is improved over the prior technology and the
modulation ratio can be minimized.
By generating the d-axis and q-axis revision voltage values vd_0*
and vq_0* in this way, the optimum output voltage command value can
be selected for each of the power sources 10a and 10b and
degradation of the power factors of the motor current command value
Idq* and the output voltage command values Vdq_a* and Vdq_b* for
the power sources 10a and 10b can be reduce. Additionally, since
the modulation ratio can be minimized, the current command value
can be reduced with respect to a given fixed power command value,
thereby suppressing the occurrence of copper loss, and power can be
transferred between the power sources 10a and 10b with a higher
degree of efficiency. As described above, larger power transfers
can be controlled than with the comparative distributed power
control because the modulation ratio can be decreased.
Third Embodiment
Referring now to FIG. 21, a power conversion system in accordance
with a third embodiment will now be explained. In view of the
similarity between the first and third embodiments, the parts of
the third embodiment that are identical to the parts of the first
embodiment will be given the same reference numerals as the parts
of the first embodiment. Moreover, the descriptions of the parts of
the third embodiment that are identical to the parts of the first
embodiment may be omitted for the sake of brevity.
The power conversion system of the third embodiment is identical to
the power conversion system of the first embodiment illustrated in
FIGS. 2 and 3 except for the control executed by the revision
voltage control section 43b of the current/power control section
43. More specifically, in the third embodiment of the present
invention, the revision voltage control section 43b of the
current/power control section 43 is configured to execute the
control operation illustrated in a flowchart of FIG. 21 instead of
the control operation illustrated in the flowchart of FIG. 4.
The flowchart for the revision voltage control section 43b executed
in the third embodiment of the present invention is shown in FIG.
21. As shown in FIG. 21, in step S30, the revision voltage control
section 43b is configured to determine whether the value of the
comparison result Pcmpa* is 1 or 0. If the comparison result Pcmpa*
is 1 (Yes in step S30), then the revision voltage control section
43b proceeds to step S31. On the other hand, if the value of the
comparison result Pcmpa* is 0 (No in step S30), then the revision
voltage control section 43b proceeds to step S32.
In step S32, the revision voltage control section 43b is configured
to set the values of the d-axis and q-axis revision voltage values
vd_0* and vq_0* to 0.
In step S31, the revision voltage control section 43b is configured
to generate the d-axis and q-axis revision voltage values vd_0* and
vq_0* based on the comparison result Pcmpa*, the d-axis voltage
command value vd*, the q-axis voltage command value vq*, the d-axis
current command value id*, the q-axis current command value iq*,
and the power command value Pb* of the power source 10b. More
specifically, the values vd_0* and vq_0* are calculated based on
the equations (5) shown below in step S31
.times..times..times..times..times..times..times..times..times..times..ti-
mes..times..times..times. ##EQU00005##
The method of deriving the above equations (5) will now be
explained. The electric power command value Pb* has the following
relationship. Pb*=id*.times.vd.sub.--0*+iq*.times.vq.sub.--0*
Equation (6)
Solving the above equation for the revision voltage value vd_0*
results in the following equation (7).
.times..times..times..times..times. ##EQU00006##
The d-axis and q-axis voltage command values vd_a* and vq_a* of the
power source 10a and the d-axis and q-axis voltage command values
vd_b* and vq_b* of the power source 10b can be expressed as follows
when the power source 10a outputs power and the power source 10b
receives the power. vd.sub.--a*=vd*.times.rto.sub.--pa+vd.sub.--0*
vq.sub.--a*=vq*.times.rto.sub.--pa+vq.sub.--0*
vd.sub.--b*=vd*-vd.sub.--a* vq.sub.--b*=vq*-vq.sub.--a*
Moreover, when the value of the comparison result Pcmpa* is 1, the
above equations can be rewritten as follows:
vd.sub.--a*=vd*+vd.sub.--0* vq.sub.--a*=vq*+vq.sub.--0*
vd.sub.--b*=-vd.sub.--0* vq.sub.--b*=-vq.sub.--0*
When the above conditions are satisfied, a value vq_0.alpha.*
corresponding to when the power factors of the motor current
command vector (Idq*) and a vector corresponding to the output
voltage command value Vdq_a* of the power source 10a being the
same, i.e., a value vq_0.alpha.* that satisfies the relationship
id*:iq*=vd_a*:vq_a*, is calculated by using the equation (8) as
follows:
.times..times..alpha..times..times..times. ##EQU00007##
Next, a value vq_0.beta.* corresponding to when the power factors
of the motor current command vector (Idq*) and a negative vector
(-Vdq_b*) (vector having the same point of origin and magnitude
directed in a 180-degree opposite direction) of a vector
corresponding to the output voltage command value Vdq_b* of the
power source 10b are the same, i.e., a value vq_0.beta.* that
satisfies the relationship id*:iq*=vd_b*:vq_b*, is calculated by
using the equation (9) as follows:
.times..times..times..beta..times..times..times..times..times..times.
##EQU00008##
The final revision voltage value vq_0* is calculated as the average
of vq_0a* and vq_0.beta.* as shown in the equation (5). After
calculating the revision voltage value vq_0*, the revision voltage
value vd_0* is obtained using the equation (6) above expressing the
relationship with respect to the electric power command value
Pb*.
.times..times..times..times..times..times..times..times..times..times..ti-
mes..times..times..times. ##EQU00009##
The d-axis and q-axis revision voltage values vd_0* and vq_0* are
set such that the motor current command vector (Idq*) lies between
the second vector (Vdq_a*) and the negative vector (-Vdq_b*) of the
first vector (Vdq_b*), where the second vector (Vdq_a*) is a vector
whose components on a d-q coordinate system are the d-axis and
q-axis voltages vd_a* and vq_a* of the power source that will
output power (e.g., the power source 10a in this example), where
the first vector (Vdq_b*) is a vector whose components on a d-q
coordinate system are the d-axis and q-axis voltages vd_b* and
vq_b* of the power source that will receive power (e.g., the power
source 10b in this example), the motor current command vector
(Idq*) is a vector whose components are the d-axis and q-axis
current command values id* and iq*, the motor voltage command
vector (Vdq*) is a vector whose components are the d-axis and
q-axis voltage command values vd* and vq*, and -Vdq_b* is a
negative vector of the first vector (Vdq_b*) (i.e., a vector having
the same point of origin and magnitude directed in a 180-degree
opposite direction from Vdq_b*). The relationships between these
vectors obtained in the third embodiment are the same as the
relationships illustrated in the vector diagram of FIG. 5. By
producing the d-axis and q-axis revision voltage values vd_0* and
vq_0* in this way, the revision voltage commands can be obtained at
any time by calculating them with a microcomputer, processor, or
other computing means and it is not necessary to depend on a preset
map. As a result, power transfers can be accomplished with a high
degree of precision.
Although the present invention is explained herein based on
drawings and embodiments, it should be recognized that one skilled
in the art can readily prepare numerous variations and
modifications based on this disclosure. For example, the power
conversion system of the present invention can be applied to both
direct current and alternating current power sources.
General Interpretation of Terms
In understanding the scope of the present invention, the term
"comprising" and its derivatives, as used herein, are intended to
be open ended terms that specify the presence of the stated
features, elements, components, groups, integers, and/or steps, but
do not exclude the presence of other unstated features, elements,
components, groups, integers and/or steps. The foregoing also
applies to words having similar meanings such as the terms,
"including", "having" and their derivatives. Also, the terms
"part," "section," "portion," "member" or "element" when used in
the singular can have the dual meaning of a single part or a
plurality of parts. The term "detect" as used herein to describe an
operation or function carried out by a component, a section, a
device or the like includes a component, a section, a device or the
like that does not require physical detection, but rather includes
determining, measuring, modeling, predicting or computing or the
like to carry out the operation or function. The term "configured"
as used herein to describe a component, section or part of a device
includes hardware and/or software that is constructed and/or
programmed to carry out the desired function. Moreover, terms that
are expressed as "means-plus function" in the claims should include
any structure that can be utilized to carry out the function of
that part of the present invention. The terms of degree such as
"substantially", "about" and "approximately" as used herein mean a
reasonable amount of deviation of the modified term such that the
end result is not significantly changed.
While only selected embodiments have been chosen to illustrate the
present invention, it will be apparent to those skilled in the art
from this disclosure that various changes and modifications can be
made herein without departing from the scope of the invention as
defined in the appended claims. For example, the size, shape,
location or orientation of the various components can be changed as
needed and/or desired. Components that are shown directly connected
or contacting each other can have intermediate structures disposed
between them. The functions of one element can be performed by two,
and vice versa. The structures and functions of one embodiment can
be adopted in another embodiment. It is not necessary for all
advantages to be present in a particular embodiment at the same
time. Every feature which is unique from the prior art, alone or in
combination with other features, also should be considered a
separate description of further inventions by the applicant,
including the structural and/or functional concepts embodied by
such feature(s). Thus, the foregoing descriptions of the
embodiments according to the present invention are provided for
illustration only, and not for the purpose of limiting the
invention as defined by the appended claims and their
equivalents.
* * * * *